Resolve #618 (Specify TZDB location via CMake)

[connorjak]

I went ahead and renamed INSTALL to TZDB_INSTALL_PATH to reduce possibility of name conflicts.

NOTE: A common issue may be that you have multiple executables with different relative paths. I resolve that by inserting a copy of the tzdata folder at the same relative path from the each executable.

Related: #618

[connorjak]

NOTE: This would require a documentation update for set_install() at https://howardhinnant.github.io/date/tz.html

[HowardHinnant]

At this time I would rather not change the API, even that of the build macros, unless it is truly urgent. The rationale for this position is that this is a period of stability for this library while C++ vendors implement and ship its C++20 equivalent. In the best of all worlds, a year from now this library will be used only for legacy projects where stability is the highest priority.

[connorjak]

Got it, I can revert TZDB_INSTALL_PATH to INSTALL.

[HowardHinnant]

Thanks.

[connorjak]

I did the revert in the latest commit; I'd say this PR is ready to merge.

[derived-coder]

Shouldn't be this in the

if( BUILD_TZ_LIB )

block?

I would put it in this line:

     if ( USE_SYSTEM_TZ_DB AND NOT WIN32 AND NOT MANUAL_TZ_DB )
         target_compile_definitions( date-tz PRIVATE PUBLIC USE_OS_TZDB=1 )
     else()
          target_compile_definitions( date-tz PUBLIC INSTALL=${USE_CUSTOM_TZDB_INSTALL_PATH} USE_OS_TZDB=0 )
     endif()

Se how I removed the other: INSTALL=. together with USE_OS_TZDB, that is IMHO an error, will not be considered

[connorjak]

Oh yeah, I should move it.